1. Field of the Invention
This invention relates to ram extruders for extrusion of plastic material such as rubber.
2. Description of the Prior Art
U.K. Pat. No. 1141033 describes and illustrates a ram extruder comprising an extruder barrel to receive a charge of material to be extruded, a die at one end of the barrel having a die opening equivalent in cross-section to the required cross-section of the material to be extruded and a hydraulic ram at the other end of the barrel having a plunger which is advanced by the ram along the barrel to extrude the material in the barrel through the die opening to be formed into an extrudate of cross-section determined by the die.
In order to load the barrel with a charge of the material to be extruded it is necessary to open the barrel at the die end and load-pre-heated charges of material to be extruded into the barrel manually after which the barrel is closed, a vacuum cap is applied enabling evacuation of air from the barrel to avoid inclusion of excessive air pockets in the extrudate. The loading of the barrel is a cumbersome and unpleasant operation since the charges of material are heavy and are also hot having been pre-heated ready for extrusion. It has been proposed to provide a screw-extruder for feeding material to be extruded to the barrel adjacent the ram end of a hydraulic ram extruder and to provide a valving arrangement for the piston or plunger of the ram to allow material to pass to the forward side of the piston as the piston retracts along the barrel after an extrusion operation. Screw-extruders however have relatively low volume flow rates and so a very substantial screw-extruder would be required to fill an extruder barrel at anything like the rate at which a hydraulic ram could empty the barrel. Moreover screw-extruders are expensive in relation to ram extruders of equivalent output and so the overall costs of a ram extruder equipped with a screw-extruder for filling the barrel of the ram extruder would be considerable. Furthermore, it is difficult to ensure even heating of the compound using a screw extruder and also the range of compounds which may be used in screw extruder is restricted.